HARQ (Hybrid Automatic Repeat reQuest) is a prior art available as a retransmission control technology in a radio communication system. For example, HARQ is used for 3GPP LTE (for example, Non-patent Documents 1 to 3).
A mobile station apparatus feeds back ACK in TB units using UCI (Uplink Control Information) if there is no error in a transport block (hereafter TB) transmitted from a base station apparatus, or feeds back NACK in TB units if there is an error. The base station apparatus transmits a new TB if ACK is received, or retransmits the same TB if NACK is received (see FIG. 18A to FIG. 18D).
In LTE, there are two types of physical channels to transmit UCI: PUSCH (Physical Uplink Shared Channel) for transmitting data signal; and PUCCH (Physical Uplink Control Channel) for transmitting control signal. If PUSCH is assigned from the base station apparatus at the timing of transmitting ACK or NACK, the mobile station apparatus transmits ACK or NACK using PUSCH. If PUSCH is not assigned, on the other hand, the mobile station apparatus transmits ACK or NACK using PUCCH.
Another available retransmission technology is that if a plurality of code blocks (hereafter CB(s)) are included in TB, the mobile station apparatus transmits ACK or NACK in CB units and the base station apparatus retransmits the data in CB units (for example, Non-patent Document 4, FIG. 19A to FIG. 19D).    Non-patent Document 1: 3GPPTS36.211 V8.3.0    Non-patent Document 2: 3GPPTS36.212 V8.3.0    Non-patent Document 3: 3GPPTS36.213 V8.3.0    Non-patent Document 4: 3GPPTSG RAN WG1 R1-062597, “Number of HARQ Channels”, Motorola